1. Field of the Invention
The invention relates generally to a hydraulic boat lift having improved reinforced concrete pilings and more particularly to a hydraulic boat lift mounted on reinforced concrete pilings wherein the lift operates with static cables and moving sheaves guided by grooves formed in the prestressed concrete pilings.
2. Discussion of the Prior Art
A variety of boat lifts or hoists are known. Heretofore, one such hoist involved a pair of davits which were secured to a dock or sea wall, and which extended out over the water. Block and tackle arrangements were carried by the end of the davits which, in turn, were connected to the bow and stern of the boat. Other boat lifting devices were known in which the above-described block and tackle arrangements were replaced by a horizontal pipe journaled on the ends of the davits, with a pair of cables, attached to the pipe at each end thereof proximate the davits, and with the cables being connected to the bow and stern of the boat. Upon rotation of the journaled pipe, as by means of a large hand wheel affixed to one end thereof, the pipe served as a winch which would uniformly raise or lower both ends of the boat substantially simultaneously.
Other boat dock and lift apparatus were known in which an upright frame was provided adjacent the water, with the frame secured to a dock or sea wall. One such device is shown in U.S. Pat. No. 4,432,664 to Baldyga which discloses a boat hoist which comprises a column, a tubular hoist sliding vertically on the column, a boat cradle on the hoist, shore reinforcement means to anchor an upper part of the column to the shore, and a power unit connecting the column and hoist. A hydraulic cylinder rests on a bottom closure plate and the cylinder contains a piston rod and serves to lift the hoist when hydraulic pressure is applied.
U.S. Pat. No. 4,509,446 to Sutton discloses a drydocking device having a moment resisting arrangement and a submersible pontoon having a first side positioned adjacent to a single fixed structure and having an arrangement for selectively introducing air or water into at least one chamber within the pontoon for raising and lowering the pontoons.
U.S. Pat. No. 4,641,596 to Reprogel et al discloses an upright frame having a pair of spaced upright members and a horizontal cross member. A lift is mounted on the frame. The lift has a support engageable with a boat hull and a pair of generally vertical arms movably mounted on the frame uprights. A compound pulley and cable arrangement is mounted on the horizontal cross members of the frame. This pulley and cable arrangement includes a first pulley block stationary with respect to the frame, and a second pulley block movable horizontally along the cross member. A first cable is secured to the frame, is entrained around certain of the pulleys on the first and second pulley block, and is secured to one of the lift uprights. A second cable is also secured to the frame, entrained around others of the pulleys on the first and second pulley blocks, and is secured to the other lift upright. A hydraulic cylinder is secured between the frame and the movable pulley block such that upon actuation of the hydraulic cylinder, horizontal movement of the second pulley block is effected along the cross member forward and away from the first pulley block to take up or let out the cables, and to move both of the lift upright members an equal distance in vertical direction along the frame uprights so as to ensure that the lift support and a boat supported thereon remain in generally horizontal position as the lift is raised and lowered.
U.S. Pat. No. 4,773,346 to Blanding et al discloses a hydraulic boat lift for lifting small boats upwardly out of a body of water simultaneously supplying water pressure to four support posts connected to four corner portions of a lifting frame. Each of the corner posts comprises a hydraulic cylinder body connected to the lift and moveable vertically on its downwardly extending piston rod which forms support legs for the lift.
U.S. Pat. No. 5,090,841 to Penick et al discloses a boat lift in which a hydraulic pump and cylinder with a piston is mounted on a manual boat lift so that the piston rod carries a pulley which engages the lifting cable so that when the piston moves in the cylinder, the boat will move up or down.